1. Field of the Invention
The present invention relates to vibrators, vibrating gyroscopes using the vibrators, and electronic apparatuses using the gyroscope.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 7-332988 describes a piezoelectric vibrator and a vibrating gyroscope using the piezoelectric vibrator. In this piezoelectric vibrator, a first piezoelectric substrate is polarized in the thickness direction and split electrodes are formed on one of the main surfaces of the first piezoelectric substrate. A second piezoelectric substrate is also polarized in the thickness direction and a common electrode is formed on one of the main surfaces of the second piezoelectric substrate. In addition, the remaining main surfaces of the first and second piezoelectric substrates are bonded to each other to constitute the piezoelectric vibrator.
The above piezoelectric vibrator has a resonant frequency and an anti-resonant frequency in each of a longitudinal vibration as a bending vibration in the thickness direction and a transverse vibration as a bending vibration in the widthwise direction. In this case, the thicknesswise direction and the widthwise direction of the piezoelectric vibrator are equivalent to the thicknesswise direction and the widthwise direction of each of the first and second piezoelectric substrates.
In the present invention, the difference between a resonant frequency and an anti-resonant frequency obtained in a longitudinal vibration of a piezoelectric vibrator is defined as a longitudinal DF, and the difference between a resonant frequency and an anti-resonant frequency obtained in a transverse vibration thereof is defined as a transverse DF.
In the related art, the material of the first piezoelectric substrate is the same as the material of the second piezoelectric substrate. In this case, in terms of the relationship between the longitudinal DF and the transverse DF in the piezoelectric vibrator, the longitudinal DF is found to be approximately twice as large as the transverse DF.
In such a piezoelectric vibrator, when depole occurs in the piezoelectric substrate even slightly due to heat shock or the like, the longitudinal DF and the transverse DF change at the same rate. When the longitudinal DF differs from the transverse DF significantly, the amounts of the changes of them are also significantly different. Thus, since the amount of change in the resonant frequency of the longitudinal vibration differs from the amount of change in the resonant frequency of the transverse vibration, the difference between the resonant frequencies of the longitudinal and transverse vibrations changes. As a result, the characteristics of the piezoelectric vibrator also change.
Accordingly, it is an object of the present invention to provide a piezoelectric vibrator whose characteristics do not change significantly even when depole occurs due to heat shock or the like. It is another object of the invention to provide a vibrating gyroscope using the piezoelectric vibrator and an electronic apparatus using the vibrating gyroscope.
According to a first aspect of the present invention, there is provided a piezoelectric vibrator including a first piezoelectric substrate polarized in the thickness direction, split electrodes formed on one of the main surfaces of the first piezoelectric substrate, a second piezoelectric substrate polarized in the thickness direction, and a common electrode formed on one of the main surfaces of the second piezoelectric substrate. The remaining main surface of the first piezoelectric substrate is bonded to the remaining main surface of the second piezoelectric substrate and the material of the first piezoelectric substrate is different from the material of the second piezoelectric substrate.
In this piezoelectric vibrator, the material of the first piezoelectric substrate is set as a first material and the material of the second piezoelectric substrate is set as a second material. The first and the second materials may be chosen such that a first difference between a resonant frequency and an anti-resonant frequency obtained in a longitudinal vibration of the piezoelectric vibrator in which the first and second piezoelectric substrates are made of only the first material is greater than a second difference between a resonant frequency and an anti-resonant frequency obtained in a longitudinal vibration of the piezoelectric vibrator in which the first and second piezoelectric substrates are made of only the second material.
In addition, the first and second materials may be chosen such that the average value of the first and second differences substantially coincides with the value of the difference between a resonant frequency and an anti-resonant frequency obtained in a transverse vibration of the piezoelectric vibrator in which the first and second piezoelectric substrates are made of the first material.
According to a second aspect of the invention, there is provided a vibrating gyroscope including the piezoelectric vibrator of the invention, a driving unit for longitudinally vibrating the piezoelectric vibrator, and a detecting unit for detecting the transverse vibration of the piezoelectric vibrator.
According to a third aspect of the invention, there is provided an electronic apparatus including the vibrating gyroscope.
With the above-described arrangement, in the piezoelectric vibrator of the invention, even when depole occurs due to heat shock or the like, there is no significant change in the characteristics.
In addition, in the vibrating gyroscope and the electronic apparatus according to the present invention, the characteristics do not change significantly due to a change in environment.